1. Field of the Invention
This invention relates to a focal plane shutter that uses an electromagnetic actuator serving as a driving source and including a rotor that rotates within a predetermined angular range.
2. Description of the Related Art
A well-known conventional focal plane shutter includes an electromagnetic actuator, which is made up of a cylindrical magnetized rotor, a yoke disposed around the rotor, a coil wound onto the yoke, etc., leading and trailing blades for opening and closing an exposure aperture, a charge mechanism for charging a spring force by which the leading blade and the trailing blade are driven, and a latch mechanism for maintaining a charged state while latching a spring. The leading and trailing blades are moved to perform an exposure operation by allowing the electromagnetic actuator to release a latched state (see Japanese Unexamined Patent Publication No. Hei-8-190123).
Another well-known conventional focal plane shutter includes leading and trailing blades for opening and closing an exposure aperture, and an electromagnetic actuator, which is made up of a cylindrical magnetized rotor, a yoke disposed around the rotor, a coil wound onto the yoke, etc., in which the electromagnetic actuator is disposed to correspond to each of the leading and trailing blades so as to directly drive the leading blade and the trailing blade (see International Publication WO02/43227).
Moreover, in the focal plane shutter structured to drive the leading and trailing blades by the charge force of the spring, there has been a need to change the wire diameter, the number of windings, etc., of the spring generating a driving force in order to change the relationship between a rotation angle and a torque. There has also been a need to adjust the running characteristics of the leading blade and the trailing blade if a desired exposure operation is not obtained or unevenness in exposure occurs.
Likewise, in the focal plane shutter structured to directly drive the leading and trailing blades by the electromagnetic actuator, there has been a need to troublesomely prepare and re-attach a new rotor that has undergone a change in its magnetization angle if a desired exposure operation is not obtained or unevenness in exposure occurs because of variation in the magnetization angle of the rotor or for other reasons.
The present invention has been made in consideration of the problems of the conventional devices. It is therefore an object of the present invention to provide a focal plane shutter capable of obtaining a desired exposure characteristic merely by performing a simple adjustment without carrying out the job of exchanging or rearranging components.
The focal plane shutter of the present invention that achieves the object has a base plate that defines an exposure aperture; an electromagnetic actuator including a rotor rotatably supported on the base plate and having a magnetized part magnetized to different polarities and an output part from which a driving force is output outward, a yoke that is disposed around the rotor and forms a magnetic circuit, and a magnetizing coil wound on the yoke; a blade supported pivotably on the base plate and connected to the output part to open and close the exposure aperture; and an angle adjusting mechanism that can adjust at least two relative mounting angles of the yoke, the magnetized part, and the output part of the rotor around a rotational axis of the rotor.
According to this structure, variation in the magnetization angle can be corrected, and the mounting angle can be changed to be a desired angular position by allowing the angle adjusting mechanism to adjust at least two relative mounting angles of the yoke, the magnetized part, and the output part of the rotor, for example, when the magnetization angle (i.e., angular position of a boundary plane between N and S poles) of the rotor with the yoke or with the output part deviates from a predetermined position or when the magnetization angle is adjusted to be the desired angular position so as to change an exposure characteristic.
In the device constructed as above, the angle adjusting mechanism can have a holding plate that holds the yoke and an adjusting mechanism that can adjust the holding plate to be situated at a desired angular position around the rotational axis.
According to this structure, the mounting angle of the yoke with respect to the magnetization angle of the rotor can be corrected or changed by allowing the adjusting mechanism to turn the holding plate around the rotational axis of the rotor so as to be situated at a desired angular position.
In the device constructed as above, the angle adjusting mechanism can have an output part formed separately from the rotor and an adjusting mechanism that can adjust a relative angular position between the rotor and the output part.
According to this structure, the mounting angle of the magnetized part with respect to the output part of the rotor can be corrected or changed by allowing the adjusting mechanism to turn the output part around the rotational axis of the rotor so as to be situated at a desired angular position.
In the device constructed as above, the blade can include a leading blade that opens the aperture and a trailing blade that closes the aperture when an exposure operation is performed, and the electromagnetic actuator and the angle adjusting mechanism can be provided for each of the leading blade and the trailing blade.
According to this structure, an exposure operation stable in, for example, slit running can be obtained by respectively driving the leading and trailing blades by use of the electromagnetic actuator having the angle adjusting mechanism.